1. Field of the Invention
The invention disclosed herein pertains to self-stacking spiral conveyor belts commonly used for freezing or cooking foods and other processing applications, and more precisely to improvements that make such belts more reliable.
2. Description of the Related Art
Endless, self-stacking conveyor belts used in the freezing and cooking food industries are described in U.S. Pat. Nos. 4,603,776; 4,941,567; 5,190,143; 5,803,232 and 6,796,420. Such conveyor belts comprise a plurality of interconnected links, each including two parallel transverse rods and a pair of upward extending side plates.
Each side plate includes an integrally formed outer one-half plate section and an inner one-half plate section. The outer one-half plate section is slightly offset outwardly with respect to the inner one-half plate section thereby enabling the inner one-half plate section on a link to extend over the inside surface of the outer one-half plate section on the adjacent link. During operation, the outer one-half plate section on a link and the inner one-half plate section on a adjacent link overlap and slide together as the belt moves along its path.
The belt travels in a straight path until it enters a spiral or helical configuration. When aligned in the helical configuration, the lower tier of the belt is supported by the drive system while the upper tiers are supported by the lower tiers. The interface between adjacent tiers is designed to keep the belt supported and laterally aligned. During use, the upper edge of the lower link contacts the bottom surface of the transverse rods on the upper tier. The tiers are laterally aligned by resting the upper edge of the lower link against the transverse rods on the upper link and by a guide tab that extends from the inner one-half plate section on the upper link.
The ends of the two transverse rods extend through elongated slots formed on the inner one-half plate sections of the left and right side plates to loosely connect the two links. Because conveyor belts are designed to be placed in a helical configuration, the slots are elongated on the side plate to which the belt turns to enable the belt to contract on that side. In the prior art, the diameter of the arc and the width of each elongated slot are slightly larger than the diameter of the transverse rod so that the transverse rod may slide freely inside the elongated slot during operation. While such movement is desirable for maximum flexibility in the belt, if the diameter of the transverse rod and the diameter and width of the elongated slot are substantially different, the amount of contact area between the transverse rod and the elongated slot is reduced, which increases the pressure exerted in specific locations on the belt which results in failure.
When moving in a helical configuration, longitudinally aligned tensile forces are applied to the belt causing it to stretch in the direction of travel. Also, when the belt travels in the helical path, the belt is stacked into circular tiers that bend the links and create stress on other components. When the belt is stacked in tiers, the contact surfaces or points between the upper and lower links in the stacked tiers are gradually worn which leads to breakage and a reduction of the overall height of the belt.
Because self-stacking conveyor belts are commonly used for freezing or cooking foods, the flow of cold or hot air through the belt and around the food products placed on the belt is an important consideration. Unfortunately, with conveyor belts found in the prior art, the flow of air is less than desirable.